In the blow moulding of plastic components of thermoplastic polymer, in particular hollow plastic bodies, for example PET bottles, so-called preforms consisting of the polymer material are heated to soften the polymer material and converted into the desired configuration by injecting gas under pressure in a mould. One measure which is frequently used among various possible ways of heating the preform is irradiation with infrared rays (IR). In that case the effectiveness of heating and thus the economy of the method are correspondingly higher, the greater the degree to which the radiation is absorbed by the polymer material and converted into heat. It may therefore be advantageous to add to the polymer material radiation absorbers which improve the radiation absorption of the material.
Materials which act as radiation absorbers in polymer materials are basically known. Problems which however can be involved with providing the polymer material with radiation absorbers are for example the lack of foodstuff compatibility or indeed the toxicity of many materials which are basically suitable as radiation absorbers, which makes them unsuitable for many uses, for example for foodstuff packagings like PET bottles. In addition materials which are basically suitable as radiation absorbers can adversely affect the properties of the polymer material, for example stability, strength and flexibility or also the barrier properties of the polymer material.
A further disadvantage of known materials which act as radiation absorbers in polymer materials is the wavelength range in which the materials can improve radiation absorption. Many radiation absorbers absorb predominantly in the shorter-wavelength IR range like for example copper hydroxide phosphate which has a relatively good absorption in the range of about 800 to 1600 nm with a maximum at about 1200 nm, but not in the longer-wavelength radiation range. When using such radiation absorbers therefore short-wave radiators are to be used, which however are generally more expensive than longer-wavelength radiators. Other radiation absorbers which in turn have good absorption in the longer-wavelength IR range from about 1600 nm and above like for example flake silicates frequently do not have good absorption in the shorter-wavelength IR range. A broader wavelength spectrum for the radiation absorber would be advantageous in order to make better use of the energy of radiators which radiate in a broad wavelength range. In particular absorption in the longer-wavelength IR range from about 1600 nm and above would be advantageous as longer-wavelength radiators are relatively inexpensively available.
In addition many radiation absorbers have an inherent colouring which when the radiation absorber is incorporated is transferred on to the polymer material and/or causes clouding of the polymer material. For example carbon black has very good absorption over the entire range of the IR spectrum, but it also has a high level of absorption in the visible range of the spectrum and thus a very high level of inherent colouring, so that its use is greatly limited.
WO-A-03/033582 describes an agent for the absorption of UV radiation on the basis of mixed cerium and titanium phosphate for incorporation into a polymer material. U.S. Pat. No. 7,258,923 describes multi-layer articles having an innermost layer of a thermoplastic polymer which contains IR-absorbent additives which are selected from borides of the transition metals and lanthanides. U.S. Pat. No. 5,830,568 describes a composite glass with an intermediate layer of PVB or ethyl vinyl acetate copolymer with functional ultra-fine metal oxide particles dispersed therein for light absorption.
Copper(II)hydroxide phosphate which in the literature is also referred to as basic copper phosphate is used as an additive in plastics for various purposes. For example in accordance with DE 3917294 and DE 4136994 it is added to plastics to make them writable by means of laser beams.
The known method of producing copper(II)hydroxide phosphate involves treating basic copper carbonate in aqueous dispersion with at least stoichiometric amounts of phosphoric acid at temperatures below 70° C., further mechanically moving the resulting reaction mixture in the same temperature range, then briefly heating it to boiling temperature and finally separating off the copper(II)hydroxide phosphate. That method is described in DE 3342292. It suffers from various disadvantages. The reaction times are extremely long, up to 12 hours, which is extremely undesirable in terms of production on a large technical scale. In addition CO2 is developed in the method, and that leads to unwanted foaming and problems in terms of working safety.
DE 10 2009 001 335 A1 describes a radiation-absorbent, plastic-based material comprising a polymer matrix with an absorber material which is contained therein and which is selected from phosphates, condensed phosphates, phosphonates, phosphites and mixed hydroxide-phosphate-oxoanions of copper (Cu), tin (Sn), calcium (Ca) and iron (Fe) and is finely distributed, dispersed or dissolved in the polymer matrix, wherein the absorber material can also be a mixture of the above-mentioned substances. Preferred absorber materials are tritin phosphate, tricopper phosphate, copper diphosphate, copper hydroxide phosphate and mixtures thereof. The described material is suitable inter alia as a packaging material for commercial products, in particular foodstuffs, or cosmetic agents, and is intended to absorb UV or IR radiation and to retain light from the visible range of the spectrum not at all or only to a slight degree and to cause as far as possible no unwanted inherent colouration or clouding of the polymer material by virtue of the absorber material.
DE 10 2010 003 366 A1 describes a matrix material of plastic, preferably of thermoplastic material, or lacquer, which contains an additive which makes it possible to trigger foaming of the matrix material by irradiation with laser light or IR light. The additive includes an absorber material which embedded or dissolved in the matrix material absorbs laser light or IR light and causes local heating in the matrix material at the location of irradiation with laser light or IR light, and a blowing agent which upon heating by virtue of the irradiation with laser light or IR light to temperatures above 50° C. produces a gas which foams the matrix material by decomposition, chemical conversion or reaction. In an embodiment the absorber material can be selected from phosphates, condensed phosphates, phosphonates, phosphites and mixed hydroxide-phosphate-oxoanions of various metals, preferably from phosphates of Cu, Sn, Fe, Ni, Mo, Co, Mn or Sb. Copper hydroxide phosphate is particularly preferred.